The use of water based paints in combination with electrostatic charging has brought about that the safety aspects have been focused, as short circuits between the high-voltage electrostatic charging in the paint gun and the grounded paint conduit system may occur.
Different devices are earlier known for preventing such potential differences to arise. All these known methods operate according to the so called "rain-drop principle", which means that the storage container, in which the paint is stored, is separated from the electrostatically charged paint gun, and supplies the paint drop by drop via such a big air-gap that no spark-over can occur. These devices however have the drawback of having a very limited capacity and do not allow a continuous spray painting, particularly if it concerns bigger painting objects, such as e.g. car bodies.
Another problem at conventional painting paints is the difficulty to change paint during the short time required for moving away the treated object and placing a new painting object within the action radius of the paint gun. As the painting ever more is carried out with aid of robots it is preferred that the paint change shall be effected without the need of changing spraying equipment.